<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>12.下拉菜单</title>
    <link rel="stylesheet" href="bootstrap-4.5.3/css/bootstrap.css">
</head>
<body>
    
    <div class="dropdown">
        <button class="btn btn-primary dropdown-toggle" data-toggle="dropdown">请选择</button>
        <div class="dropdown-menu">
            <div class="dropdown-item">选项一</div>
            <div class="dropdown-item">选项二</div>
            <div class="dropdown-item">选项三</div>
        </div>
    </div>



    
    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"  ></script>
    <script src="./bootstrap-4.5.3/js/bootstrap.js"></script>
</body>
</html>